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NCP1601A

Compact Fixed Frequency Discontinuous or Critical Conduction Voltage Mode Power Factor Correction Controller

ON Semiconductor 

NCP1601A, NCP1601B

FUNCTIONAL DESCRIPTION

Introduction

The NCP1601 is a Power Factor Correction (PFC) boost

controller designed to operate in Discontinuous

Conduction Mode (DCM) and Critical Conduction Mode

(CRM). The fixed−frequency nature of DCM limits the

maximum switching frequency. It limits the possible

conducted and radiated EMI noise that may pollute

surrounding systems. NCP1601 offers the simplest solution

to PFC including fewer external circuit components and

simple voltage−mode feedback. The diode turn−off

switching loss is negligible and hence there is no need to

use a low reverse−recovery time trr diode. On the other

hand, the CRM feature is added to limit the maximum

current stress to twice of the average current. The NCP1601

incorporates high safety protection features and combines

the advantages of DCM and CRM so that the NCP1601 is

suitable for robust and compact PFC stages.

The NCP1601 provides the following protection features:

1. Overvoltage Protection (OVP) is activated and

the output drive goes low when the output voltage

exceeds 107% of the nominal regulation level

which is a user−defined value. The circuit

automatically resumes operation when the output

voltage becomes lower than 107%.

2. Undervoltage Protection (UVP) is activated and

the device is shut down when the output voltage

goes below 8% of the nominal regulation level.

The circuit automatically resumes operation when

the output voltage goes above 8% of the nominal

regulation level. This feature also provides output

open−loop protection and external shutdown

feature.

3. Overcurrent Protection (OCP) is activated and

the output device goes low when the inductor

current exceeds a user−defined value. The

operation automatically resumes when the

inductor current becomes lower than this

user−defined value at the next clock cycle.

4. Thermal Shutdown (TSD) is activated and the

output drive is disabled when the junction

temperature exceeds 140°C. The operation

resumes when the junction temperature falls

down by typical 45°C.

The NCP1601 is available in two versions. The

NCP1601A has a typical 4.75 V undervoltage lockout

(UVLO) hysteresis, while NCP1601B has a typical 1.5 V

UVLO hysteresis. It allows the use of different VCC biasing

schemes.

Operating Modes of NCP1601

The NCP1601 is a PFC driver primarily designed to

operate in fixed−frequency DCM. In the most stressful

conditions, CRM can be an alternative option which is

without power factor degradation. On the other hand, the

NCP1601 can be viewed as a CRM controller with a

frequency clamp (maximum switching frequency limit)

alternative option which is also without power factor

degradation. In summary, the NCP1601 can cover both

CRM and DCM without power factor degradation. Based

on the selections of the boost inductor and the oscillator

frequency, the circuit is capable of the following three

applications.

1. “Mostly in CRM” with a frequency clamp set by

the oscillator or synchronization frequency.

2. “Mostly in fixed−frequency mode DCM” and

only run in CRM at high load and low line.

3. “Fixed−frequency DCM” only.

Current

Inductor current, IL

Input current, Iin

time

DCM

Critical Mode

DCM

Figure 25. Operating Modes

DCM needs higher peak inductor current comparing to

CRM in the same averaged input current. Hence, CRM is

generally preferred at around the sinusoidal peak for lower

the maximum current stress but DCM is also preferred at

the non−peak region to avoid excessive switching

frequencies. Because of the variable−frequency feature of

the CRM and constant−frequency feature of DCM,

switching frequency is the maximum in the DCM region

and hence the minimum switching frequency will be found

at the moment of the sinusoidal peak.

DCM PFC Circuit

A DCM/CRM PFC boost converter is shown in Figure 26.

Input voltage is a rectified 50 or 60 Hz sinusoidal signal. The

MOSFET is switching at a high frequency (typically around

100 kHz) so that the inductor current IL basically consists of

high−frequency and low−frequency components.

Filter capacitor Cfilter is an essential and very small value

capacitor in order to eliminate the high−frequency content

of the DCM inductor current IL. This filter capacitor cannot

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